The use of layered data communications protocols promotes system interoperability, vendor portability and simplicity in system integration. Each protocol layer operates at a different layer of abstraction and performs different types of data manipulation and formatting. Because each layer is concerned with events at its own level of abstraction, different software designers can work together to design the protocols. Layers of the network protocol can also be replaced individually without significant communication incompatibilities problems arising.
The Internet Protocol (IP) stack is a widely used layered communication protocol. Applications use the IP stack to transmit and receive data over a variety of different local and wide area networks. Typically, a transmitting application passes application data to a transport layer in the IP stack, which in turn adds routing information to the data and passes the results to a data link layer. The data link layer also adds additional header information and passes the resulting information to a physical layer, where it is finally transmitted over the network.
A receiving application associated with a receiving IP stack receives and processes the information. Each layer of the receiving IP stack performs various communication functions and format conversions in reverse going from the physical layer, the data link layer, the network layer, the transport layer, and then to the receiving application. In a conventional network, applications send and receive messages from each other and use the IP stack as a conduit for data. Notwithstanding these messages, other information being transmitted between the sending and receiving IP stacks is not typically made available to either the sending or receiving applications.
While layered protocols such as used in a conventional IP stack have some advantages, they are have been obtained by lowering programmatic flexibility. For example, application data is encapsulated with protocol-generated headers whose content cannot be accessed and controlled by the application itself. Applications are masked from the inner operation of a network protocol and network operation. This inflexibility makes it difficult for an application to send data encapsulated with a non-standard header when required or monitor operation of the network.